To determine the angular position of such a wheel, it is known from EP Patent 0952426 to provide the latter with a surface layer made of a particular material, and a with through aperture located in an intermediate area between the axis of rotation of the wheel and its circumference. A proximity sensor, which is static with respect to the wheel, is positioned directly above or below the aperture when the wheel is in a reference position. This sensor is capable of sensing the particular material and of providing a measurement signal dependent on variations in the proximity of said material. Thus, the measurement signal has a particular shape when the aperture passes above the sensor, for example a peak.
To determine an angular position in which the wheel is located, it is proposed to make the wheel complete one stepwise rotation by means of a stepping motor, while recording the measurement signal. The aforementioned peak thus indicates the passage of the wheel through its reference position. Once the reference position has been identified on the graph representing the measurement signal, it is easy to deduce therefrom the angular position of the wheel corresponding to another point on the graph, in particular, the initial angular position of the wheel, i.e. its position before it starts the rotation.
EP Patent 0952426 proposes to use an inductive sensor or a capacitive sensor, while specifying, however, that a capacitive sensor is more sensitive to the environment and to disturbances caused by manufacturing and assembly tolerances than an inductive sensor. A capacitive sensor is in particularly affected by endshake, in the direction of the axis of rotation of the wheel, between the wheel and the sensor. The greater this endshake, the broader the peak: the precision of detection of the angular reference position is thus directly affected by endshake.